Unlike the capillary wick in a conventional heat pipe, the pumping rate across the membrane in an osmotically pumped heat pipe does not automatically match the heat input rate. Thus, if too much heat were applied to the evaporator, too much solvent would be boiled off from the solution to dry out the evaporator because the pumping of solvent through the membrane would not be sufficient to keep up with the heat input. The result would be an ever increasing overheating and eventual destruction of the device. On the other hand, if too little heat were applied to the evaporator, the continual pumping of solvent through the membrane would eventually flood the evaporator, and solution would overflow into the solvent vapor and condensate return path to contaminate the solvent with solute. Thus, such heat pipes are limited to a single heat input within 1/2 watt power.
Conventional solutions to this problems are the use of a mechanical valve to produce pressure retarded osmosis or a device to regulate the heat power. In general, a mechanical valve is too complex and expensive to be implemented within the inside of an osmotic heat pipe.